Frangible target



April 7, 1964 R. J. HOPPER FRANGIBLE TARGET 5 Sheets-Sheet 1 Filed Dec. 28, 1955v INVENTOR zW ATTORNEY ROBERT J. HOPPER,

April 7, 1964 R. J. HOPPER 3,123,463

FRANGIBLE TARGET Filed Dec. 28, 1955 5 Sheets-Sheet 2 POEERT J. HOPPER,

IN VE N TOR.

A T TORNE X April 7, 1964 R. J. HOPPER 3,128,463

FRANGIBLE TARGET Filed Dec. 28, 1955 5 Sheets-Sheet 5 ROBERT J. HOPPER,

- I INVENTOR.

A TTORNE Y.

April 7, 1964 R. J. HOPPER FRANGIBLE TARGET 5 Sheets-Sheet Filed Dec. 28, 1955 ROBERT J. HOPPER,

INVENTOR ATTORNEY.

A nl 7, 1964 R. J. HOPPER FRANGIBLE TARGET 5 Sheets-Sheet 5 Filed Dec. 28, 1955 ROBERT J. HOPPER,

INVENTOR.

ATTORNEY.

United States Patent 3,128,463 FRANGLE TARGET Robert I. Hopper, Pacific Palisades, Calif., assignor to Del Mar Engineering Laboratories, Los Angeles, Calif, a corporation Fiied Dec. 28, 1955, Ser. No. 555,858 14- Claims. Cl. 343-18) This invention relates to aerial targets and more particularly to such a target which is towed by one aircraft and used to train pilots of other aircraft in automatic fire control equipment.

The target of the present invention, in all embodiments illustrated, comprises a modified form of the target shown and described in my copending application Ser. No. 471,234. The illustrated embodiments of the target of my previously filed application, as well as the embodiments herein shown, are primarily useful in training pilots of fighter or attack aircraft in the use of automatic fire control equipment.

Such fire control equipment as presently used, whether it be rocket, cannon, or machine gun is governed or controlled by automatic systems incorporating electronic tracking devices. Novice pilots are thus initially trained in the use of this equipment by the automatic control systems which allow the pilot to make interceptor runs on a simulated enemy aircraft.

In the previously used training programs, notwithstanding the safety measures undertaken, malfunctioning systems and equipment, and inexperience of the pilots undergoing training, produced collisions between the aircraft and the simulated enemy resulting in damage to or destruction of the aircraft and, in many cases, death of the pilot undergoing training.

The target disclosed by my copending application above identified, although it did not eliminate the danger of the aircraft colliding with the simulated enemy in flight, did obviate the danger to the pilot undergoing training, for the target was so formed as to disintegrate if struck by the aircraft. This was brought about by forming the target body of a material having low impact resistance and a relatively high volume-weight ratio, such as one of the rigid cellular or foamed plastics. Aerial targets of my prior application may be towed by conventional light weight tow lines and, through the use of internal radar reflectors, made available to the Air Force, an efficient target which could be used with little or no danger to the novice pilot undergoing training. Such targets are being used in ever increasing numbers and are inherently expendable because of their function in the training programs.

Although the forms of the target shown in my copending application solve the problems inherent in prior training programs such targets were somewhat costly because of the material used and entailed the use of relatively slow production processes, which also increased the ultimate cost of the target. The embodiments of the target of the present invention, although they retain all of the advantages and features of the forms of the target described in my copending application, represent a decided advance in the art as they can be manufactured at a lower cost and at a higher production rate than the targets of my previously filed application.

All embodiments of the target herein disclosed and claimed comprises a hollow, streamlined body member of an aerodynamically stable configuration formed of at least two body shells having relatively thin or tenuous walls. The body shells are each formed of a material having a low resistance to penetration by objects making impact therewith and the body member formed thereby has a low volume-mass ratio for low inertia resistance to Patented Apr. 7, 1964 "ice avoid damage to aircraft making inadvertent impact therewith.

The target includes an internally mounted reflector unit for reflecting exteriorly propagated waves, such as used in radar systems. The reflector unit preferably comprises a plurality of sheets of metallic foil mounted by means of a support member formed of a low density material which acts to support the foil to provide at least three normally intersecting surfaces. Neither the foil sheets or the support means therefor present a hazard to an aircraft even if a collision should occur between the aircraft and the target.

Although the support element for the foil sheets is formed of a low density material, this support element nevertheless will act to internally reinforce the body shells and, in all embodiments of the target, are used to interconnect adjoining body shells to form thehollow, streamlined, elongate body member of the desired aerodynamically stable configuration.

In several embodiments herein shown, the body shells are formed of a material which does not have sufiicient strength to maintain the areodynamic configuration desired, or does not have sufiicient strength to take the air loads imposed in the towed flight of the target. In such embodiments of the present invention, the target body is reinforced by internally pressurizing the same and to this end, means are provided for introducing air under pressure into the body, the latter being heremetically sealed to prevent the escape of the air. In other embodiments of the invention shown, the material used to form the body shells has the requisite strength to both maintain the desired configuration and to take the air loads imposed as the target is towed, but yet is such that the desired low volume-mass ratio of the body member is maintained. The body shells in all embodiments illustrated are molded or otherwise formed by high production methods and subsequently assembled with the support element of the reflector unit. Internal reinforcing bulkheads or the like, if desired, can be employed in all forms of the invention shown and where used are formed of a low density, low strength material which does not present a hazard to inadvertently colliding aircraft.

The body shells in some forms of the aircraft herein shown include integral formations for providing, when the shells are assembled, fins for stabilizing the target in towed flight. In other embodiments herein disclosed, the stabilizing fins are separately formed of a low density material and subsequently assembled with the body member.

The fins are preferably cambered to produce, as the target is towed, uniform velocity of rotation of the target about its longitudinal axis. As the fins used produce rotation of the target in flight, the balance of the body member in terms of center of gravity and eccentricity of balance is far less critical than non-rotating targets of my prior application and the target of the present invention thus lends itself to mass production methods where critical tolerances of weight and balance are not easily controlled.

Other features and advantages of the present invention will be hereinafter apparent from the following description, particularly when taken in connection with the accompanying drawing, in which FIGURE 1 is a View partly in section and partly in elevation showing one embodiment of the target of the present invention;

FIGURE 2 is a fragmentary sectional view on an enlarged scale showing the nose section of the target of FIGURE 1;

FIGURE 3 is a fragmentary sectional view on an enlarged scale illustrating a detail of construction of the target of FIGURE 1;

en ages FIGURE 4 is an exploded view showing the reflector unit of the present invention;

FIGURE 5 is a section taken along line 5-5 of FIG- URE 1;

FIGURE 6 is a fragmentary view in section showing, on an enlarged scale, an internal bulkhead arrangement;

FIGURE 7 is a view similar to FIGURE 5, but showing a modified form of a fin;

FIGURE 8 is a sectional view of a portion of a modified form of the target showing the nesting arrangement of the portion illustrated:

FIGURE 9 is a view similar to FIGURE 8 but showing another portion of the target with the parts internested;

FIGURE 10 is an exploded view showing a modified form of the target;

FIGURE 11 is a view partly in section and partly in elevation of a further modified form of the target;

FIGURE 12 is a fragmentary view in section showing the nose portion of the target of FIGURE 11;

FIGURE 13 is a section taken along the line 13I3 of FIGURE 11;

FIGURE 14 is a sectional view showing a modified form of the target of FIGURE 11;

FIGURE 15 is an elevational view of a further modified form of the target of the present invention;

FIGURE 16 is a sectional View taken along line Id-Id of FIGURE 15;

FIGURE 17 is a sectional view taken along line 1717 of FIGURE 15;

FIGURE 18 is a section taken along line 18-48 of FIGURE 15; and

FIGURE 19 is a section taken along line I9I9 of FIGURE 15.

The target of the present invention, and particularly the embodiment shown in FIGURES 1 through 6 of the accompanying drawing, comprises a body member 1'3 formed of a plurality of body shells II, 12, I3 and 14 which are longitudinally interconnected to form the body member 10. It will thus be seen that the body member 10 formed by the assembled shells comprises a hollow, thin-walled, streamlined, elongate member of an aerodynamically stable configuration. Each of the body shells are preferably formed of a non-metallic material having a low resistance to penetration by relatively heavy objects making impact therewith. In the now preferred embodiment of the target shown in FIGURE 1, the body shells are molded under heat and pressure of a suitable paper pulp. The shells once formed are then impregnated with a suitable waterproofing agent, which when set and hardened not only Waterproofs the shells, but also forms a relatively smooth surface exteriorly of the shell walls.

The body shell 11, as clearly shown in FIGURE 1, is somewhat conical in shape and open at the one end, while body shells 12 and 13 are annular in configuration. The forward or leading edge of the body shell 12, during the molding process, is formed with an offset portion I5 of reduced diameter which terminates in an inturned flange 16 forming a circumferentially extending strengthening rib internally of the assembled body member. The olfset portion 15 of the shell 12 nests within the open end of the body shell 11 and the faying surfaces are joined through a suitable waterproof cement or bonding agent.

The normally trailing edge of the body shell 13 is formed with an offset portion 17 and inturned flange 18 substantially identical to the corresponding elements 15 and 16 of the body shell 12. The offset portion 17 is telescopically mounted within the open end of the body shell 14 with the faying surfaces again bonded through a suitable waterproof cement or bonding agent.

To longitudinally interconnect the body shells 12 and 13 it is now preferred, in the embodiment of the invention now being described, to use the support element 19 of a reflector unit 21. This reflector unit 21, referring now to FIGURE 4 of the drawing, includes the support element 19 which comprises a pair of identical members 22 preferably formed of a low density material having an extremely high volume-weight ratio, such as a foamed or expanded plastic. A number of present day plastics can be used and these plastics, through a suitable foaming agent, can be foamed or expanded to form a low density cellular mass. Such a foamed plastic, although frangible, is yet sufliciently rigid to hold a formed shape. The support element 19 of the present invention has been formed of foamed cellulose acetate and polystyrene with excellent results. The density of the foamed or expanded plastic can be varied and the support element should have such a density as to substantially disintegrate under impact blows such as are encountered when an aircraft inadvertently collides with the target.

The members 22 of the reflector unit each comprise a relatively thick disc portion 23 having a cylindrical edge surface 23a and a uniplanar face 23b. A semi-circular formation 24 normally projects from the one face of each disc portion 23 and centrally spans the same as clearly shown in FIGURE 4. Formations 25 arranged normal to the formation 24 on opposite sides thereof complete the member 22. The members 22 may be formed either through a molding process or by machining a preformed mass of the expanded plastic to the desired shape and configuration.

Each member 22 is formed, as by radial saw cut, for example, with relatively thin semi-circular recesses 26 extending inwardly of the face 2312 which are arranged normally to each other centrally of each member. In the assembly of the reflector unit 21, semi-circular metallic foil sheets 27 of low strength are inserted into the recess 26, each foil being formed with slots 28 to permit the foil sheets to be inserted into the normally extending recesses 26. A sheet of metal foil 2%, circular in plan form, is positioned between the planar faces 23b of each element 22, after which the faces are bonded together through a suitable cement to hold the elements 22 with the surfaces 23b thereof concentric.

It will now be seen that the reflector unit 21 comprises a plurality of sheets of a metallic foil so supported by the element 22 as to provide a plurality of reflective radar traps, each being of generally concave configuration and, in this instance, comprising a group of three normally related reflecting surfaces. Each of these radar traps faces in an outward direction at an angle to the longitudinal axis of the target body, the outward direction of the radar trap being taken at equal angles to the three reflected surfaces. Such a reflector unit forms an efficient means for reflecting propagated or transmitted waves, such as used in current radar systems, but yet does not reinforce the body of the target against disintegrating impact forces.

It will be seen, referring again to FIGURE 1, that the cylindrical surface presented by the surfaces 23a of the assembled elements 22 has a diameter substantially equal to the inner diameter of the body shells 12 and 13 to permit each body shell to be telescopically received about the reflector unit 211. The faying surfaces of the body shells 12 and 13 and the reflector unit are bonded together by a suitable cement to thus longitudinally interconnect the body shells 12 and 13 to complete assembly of the body member of the target.

To increase the bonding area it is now preferred to form, at the outer ends of the formations 24 and 25 of the members 22, enlarged portions 33 presenting surfaces which form a continuation of the cylindrical surface 23a. The enlargements 33, as best seen in FIGURE 4, are circumferentially spaced about the members 22 and present spaced apart surfaces bonded to the shells to augment the interconnection afforded by the bonding agent or cement used to hold the body shells 12 and 13 longitudinally interconnected.

Although the body portion of the reflector unit 21 is formed of a low density foamed plastic, it does, nevertheless, act to internally reinforce the body shells 12 and 13 and thus tends to strengthen the body member once the assembly operation is completed.

If desired, the aft or trailing portion of the body member may be further internally braced by bulkheads 34 or the like, which may be arranged transversely of the body shell 14 at spaced stations therealong. In the now preferred practice of the invention, the bulkheads 34 may comprise plate elements 35 and 36 of .corrugated paper facewisely bonded to each other, as best shown in FIG URES 1 and 6, but with the corrugations of each plate arranged normal to the other. To mount the bulkhead at the desired station in the tail or trailing body shell 14, a portion of the peripheral edge of each corrugated sheet is laterally offset to form a mounting tab-like element 37 which is secured or bonded to the internal surface of the body shell by suitable cement or bonding agent indicated at 38 in FIGURE 6 of the drawing.

It is now preferred to use two of such bulkheads with the one bulkhead mounted transversely of the body shell 14 adjacent the point of attachment of a plurality of stabilizing fins 39. The fins 39 are aflixed to the body member adjacent the trailing portion of the same, and these fins, referring now to FIGURE 5, are each identical in shape and contour and are preferably formed of a low density foamed plastic on the order of the plastic used to form the support element of the reflector unit. The root portion of each fin is molded or otherwise formed with an end surface 41 complementary to the shape and configuration of the exterior wall surface of the body shell 14. The fins 39 are thus separately formed from the body shells and are aflixed in the proper spaced relationship thereto by bonding the end surfaces 41 to the external surface of the body shell 14 by suitable cement or bond ing agent. To augment the union between the fins 39 and the body member 10, strips 42 of a pliant material may be partially embedded along the opposite sides of the fins at the root portion to provide anchoring elements extending longitudinally of the fins and having outwardly extending portions 43 also bonded to the exterior surface of the body member. The flexible strips 42 may be formed of a suitable cloth or like material having suflicient strength to aid in distributing loads taken by the fins 39 in the towed flight of the target into the body member 10.

The fins 39 are formed of such an aerodynamic shape as to produce substantially uniform velocity of rotation of the target on its longitudinal axis as the target is towed. In the illustrated embodiment of the invention, the trailing portion of each fin is formed with an angularly deflecting tab 44 or the like and the angular relationship of the tab 44 with the body of the fin 39 will, of course, determine the rotational force aerodynamically imposed on the body member as the target is towed. The fins 39 not only stabilize the target in flight and produce the rotation thereof about its longitudinal axis, but also results in the further feature of reducing the cost of the target. This is so, for the balance of the target in terms of center of gravity and eccentricity of balance is far less critical because of the use of the cambered fins than is otherwise possible if the target was of a non-rotating type. It is thus easier to produce the target of the present invention by mass production methods where critical tolerances of weight and balance cannot be adequately controlled.

A highly important effect of rotating the target about its longitudinal axis is that rotation of the radar corner reflectors causes radar signals to be reflected in a highly advantageous manner. One of the advantages is the kind of reflection behavior of the tow target that is characteristic of an actual enemy aircraft. The inevitable slight oscillations and fluctuating directional changes of an aircraft in flight causes corresponding changes in position and effectiveness of the corner reflecting surfaces of the aircraft, and the present rotating tow target has the same appearance on a radar screen.

Another problem is to make sure that the reflectivity of the two target does not exceed the reflectivity that would be met in actual warfare. It should be just as difficult to detect a tow target for practice as to detect an actual aircraft in warfare. The rotation of the target prevents prolongation of any reflection of peak magnitude. In this regard it is to be borne in mind that the ratio of the intensity of a reflected radar signal from a corner reflector relative to the intensity of the incident radar signal varies with the direction of the incident signal relative to the corner reflector.

Another advantage provided by rotating the described tow target is that the intensity of the reflected radar signal pulsates at a frequency equal to the rpm. of the tow target times the number of corner reflectors around the .circumference of the tow target. This frequency is known in advance since the rpm. of the target at a given speed of flight of the aircraft is known. Thus, in target practice the pilot may be sure he is intercepting the tow target and is not inadvertently attacking the towing aircraft or any other aircraft.

As the target does rotate in flight it is now preferred to provide means for attaching the target to a tow line which will not interfere with the rotational movement of the target. This means, in the illustrated embodiment of the present invention, referring now to FIGURE 2 of the drawing, comprises a swivel element generally designated by the reference character 45 and includes bearing assemblies 46 which rotatably mount an eye bolt 47 or the like within the bore of a tubular tension member 43 coaxially mounted within the body member at the leading or nose section thereof. To hold the bearing assemblies 46 against movement relative to the tubular member 48, retaining rings 4? are mounted in circumferentially extending, spaced grooves formed in the interior wall of the member 48.

The inner end of the tubular member 48 projects through an opening centrally formed in a pressure plate 51 and is anchored thereto by any means desired. This plate engages the end face of a conical plug-like element 52 mounted within the nose section of the target body and having a longitudinal passageway receiving the tubular member 48. The plug element 52 is preferably formed of a low density material, such as a'foamed plastic, and has such a configuration as to fill the nose portion of the target. It will be seen that tension loads in the towline are taken through the eye bolt 47 and bearing assemblies into the tubular member 48 and are transmitted by means of the plate 51 and plug 52 into the Wall of the body shell 11 forming the leading portion of the target body. To strengthen and integrally reinforce the pressure plate 51 it is now preferred to dish or offset the central portion of this plate as shown in FIGURE 2.

It has been found in practice that the target being described is more effectively towed in flight if the center of gravity of the target is located toward the leading or nose section of the target. To bring about this location of the center of gravity, it is now preferred to provide a mass of material, such as sand, within the portion of the target body formed by the shell 11. This may be conveniently accomplished by mounting a disc 53 of a foamed plastic in facewise engagement with the inner surface of the pressure plate 51 and bonding the peripheral surface of the disc 53 to the inner surface of the body shell 11. A quantity of sand 54 is now placed into the body shell when the same is in an erect or vertical position, after which a second disc 55 is inserted within the shell and its peripheral edge face bonded to the inner wall surface of the body shell. It will now be seen that the discs 53 and 55 effectively trap the mass of sand 54 in the chamber formed by the two discs.

The mass of sand 54 held between the two spaced discs 53 and 55 render the target somewhat nose heavy, but yet does not present any hazard to an aircraft inadvertently colliding with the target. This is so, for if the body shell 11 should be ruptured by such an impact, the sand,

r in the Lombard et al. Patent No. 2,58l,42l.

of course, readily escapes and does not form a dense mass to damage the aircraft or the power plant thereof.

If desired the stabilizing fins used may be formed, referring now to FIGURE 7 of the drawing, of a molded or otherwise formed paper shell 56 of the desired aerodynamic shape. The shell 56 can be formed of the same pulp material used to form the body shells and is also impregnated with a suitable waterproofing compound. The shell is closed at the root portion by wall element 57 having the exterior surface thereof of the same shape and configuration as the surface of the target body to permit the fin to be bonded to the body member through a suitable cement or bonding agent. The shell 56 is internally reinforced by a network 58 of spanwisely and chordwisely interconnected shear webs as clearly shown in FIGURE 7. The interconnected network of shear webs may be formed of corrugated paper plates interconnected in any manner desired to form the reinforcing network.

The shell 56, forming the body of the fin, could be filled, if desired, with paper honeycomb of the type shown In this embodiment of the fin, the trailing portion would be also formed as in the earlier described embodiment of the fin to produce the rotational forces in the target as it is towed in flight.

In the form of the target just described, it is contemplated that the target would be completely assembled at its point of manufacture and would be shipped in the assembled form to its point of use. Where found desirable, the target of the present invention may be so constituted as to permit the target to be assembled at a station other than the point of manufacture. Such an embodiment of the present invention is illustrated in FIGURES 8 through 10 of the drawing, and in this form of the invention, the target body includes a body shell 61 forming the nose portion of the target body, an intermediate body shell 62, and a trailing or end cone shell part 63.

The body shell 61 is preferably molded of a suitable paper pulp product to the desired configuration. The body shell 61 differs from the body shell 11 of the previously described embodiment merely in the axial or longitudinal length of the shell 61. Thus the shell 61 mounts a swivel assembly identical in all respects to the assembly shown in FIGURE 2 of the drawing. As the shell part is hollow and open at the one end, a series of such shells may be internested in the manner shown in FIG- URE 8 to permit shipment of a plurality of these shells in a single shipping container.

The body shell 62, which forms an intermediate section of the assembled target body is also formed of a paper pulp product through a suitable molding process. Here again the shell 62 may be internested, as illustrated in FIGURE 9, to permit shipment of a plurality of the shells in a nested arrangement within a single shipping container.

The body shell 63, like body shells 61 and 62, would also be formed of a paper pulp product by means of a suitable molding process and would comprise basically an open-ended hollow, conical section of the configuration shown in FIGURE 10. Stabilizing fins 64 would be affixed to the body shell 63 to perform the same function as the fins 39 of the embodiment of the invention shown in FIGURE 1. The fins 64-, if desired, could be of the construction illustrated in FIGURES and 7 of the drawing and secured to the body shell 63 in the manner in which the fins of FIGURES 5 and 7 are mounted to the target body as hereinbefore explained. A plurality of the body shells 63, with the fins 64 attached, could be shipped to a point of use or assembly of the target in a single shipping container or the fins could be shipped separately and subsequently affixed to the shells.

To complete the assembly of the target in the now preferred practice of the invention, it is intended that reflector units identical to the reflector unit 21 would be used to interconnect the body shells 61 and 62. The larger diametered end of the body shell 62, as well as the open end of the shell 61, present an internal cylindrical wall surface equal in diameter to the diameter of the surfaces 23a of the reflector unit 21. This configuration permits a reflector unit 21 to be telescopically inserted into the ends of a pair of body shells 61 and 62, after which the contacting surfaces of the shells and reflector unit would be bonded together through the use of a suitable cement or bonding agent. This, as will now be understood, longitudinally interconnects the body shells 61 and 62 with the contiguous end surfaces of the shells 61 and 62 in an abutting relationship. The shell part 63 is in turn connected to the smaller diametered end of the body shell 62 through a tapered plug 67 having a configuration identical to the internal tapered configuration of the contiguous portions of the body shells 62 and 63. Thus, to complete the assembly of the target the plug 67 would be telescopically fitted within adjacent ends of the shells 62 and 63 and the faying surfaces bonded together by means of a suitable bonding agent.

The plug 67 preferably is formed of a low density, foamed plastic sufficiently rigid to form the interconnecting element between the shells 62 and 63, but yet presenting no hazard to an aircraft colliding with the target. It furthermore will be seen that the plug 67 internally braces and reinforces the target body at the jointure efl ected by the plug. Thus the plug 67 will act to reinforce the target body adjacent the station thereon subject to stresses produced by the fins 64 in the towed flight of the target.

In the embodiment of the target shown in FIGURE 11 of the drawing, the body member 71 is formed of a pair of body shells 72 and 73. The body shells again are interconnected by means of an internal reflector unit 74 basically similar to the reflector unit 21 previously described. The reflector unit 74 here again presents an external cylindrical surface of the same diameter as the internal cylindrical wall surface of each body shell adjacent the open ends thereof. The open ends of the body shells are telescopically fitted over the reflector unit with the faying or contacting surfaces again bonded to hold the shells assembled in longitudinal alignment to form the body of the target.

In this form of the target, the shells 72 and 73 may be formed of cloth, impregnated with a filler which would seal the wall of the shell against passage of air, or of a glass fiber resinous composition and molded under heat and pressure to the desired configuration. Where the shell parts are formed of an impregnated cloth, formretaining reinforcing bulkheads 75 could be mounted transversely of either one or both of the body shells. In the illustrated embodiment of this form of the target, only one such bulkhead is shown and the peripheral edge of this bulkhead would be bonded, as illustrated, to the internal wall surface of the shell part 73. The target of the embodiment of FIGURE 11 again is fitted with stabilizing fins 76 which, as shown in FIGURE 13, may comprise fins identical to the fin illustrated in FIGURE 5 of the drawing. The fin 76 thus may be formed of a low density foamed plastic affixed to the target body by a bonding agent between the root end face of the fin and the surface of the body member 71. Here again this union can be augmented by strips 77 of a suitable cloth or the like similar to the strips 43 of the previously described embodiment.

To reinforce the section of the target body carrying the fins 76, an elongate filler element 7 3 can be used. This filler element may also be formed of a low density foamed plastic having a density on the order of the support member 22 of the reflector unit 21 previously described. The filler element 78, as clearly shown in FIGURE 11, is intended to completely fill the trailing portion of the target body and is preferably bonded to the internal wall surface of the body shell 73 by some suitable bonding agent.

Where the shell parts are formed of an impregnated cloth, the cloth need not be sufiiciently rigid to maintain the desired configuration for this practice of the invention envisions the use of a compressed fluid, such as compressed air, to internally reinforce the wallof the target, as well as to maintain the assembled target in the desired elongate, streamlined configuration. To this end, the embodiment of the invention now being described includes an air valve 79 of the Schroeder type carried by the shell 73 at the end thereof which permits air under pressure to be introduced into the target body.

The plug 78 is formed with a longitudinally extending passageway 81 to permit passage of the air through the filler element, the bulkhead 75 and the reflector unit 74 also being formed with passages 82 and 83, respectively, to permit the entire target to be filled with air under pressure. The internal pressure of the air, as will be understood, not only reinforces the shell walls, but also acts where the shells are formed of an impregnated cloth to maintain the desired elongate streamlined configuration of the target body.

The target of FIGURE 11 is also intended to be rotated in flight and this is accomplished through a swivel assembly 84 which includes an eye bolt 85 or the like rotatably mounted through bearing assemblies 86 fixed within a tubular element 87 coaxially mounted at the nose of the target. In this form of the swivel assembly, the tubular element 87 is closed at the inner end thereof and is welded or otherwise secured to a pressure plate 83 which facewisely engages a conical plug member 89 formed of a low density foamed plastic filling the nose portion of the target and having the surface thereof bonded to the internal wall surface of the shell part 72. The bonding of the element 88 to. the internal wall surface of the shell 72 seals the jointure therebetween against the passage of air forwardly of the plug 89.

To further insure against air leakage from the assembled target, the wall of the shell part 72 may include a short tubular extension sleeving the leading end of the tubular element 87 and bonded thereto. To relieve this sealed joint from all stresses, a ring 91 circumscribes the tubular extension of the shell part 72. Although not shown, the band 91 may comprise a clamp element which can be clamped or compressively engaged about the tubular extension of the shell to compressively hold the same against the tubular element 87. The swivel assembly 84 functions in the same manner as the assembly 45 and, as should be understood, will act with its associated element to carry the tension loads from the tow cable into the wall of the body member 71.

Where the form of the target shown in FIGURE 11 is formed with a glass fiber impregnated molded part, the portion of the wall of the trailing body shell to which the fins are attached may be integrally reinforced and strengthened by thickening the wall portion throughout the extent of the body member to which the stabilizing fins are attached. Such an expedient is illustrated in FIGURE 14 of the drawing wherein the wall of the body shell 92 is increased in thickness as indicated at 93 to strengthen the body shell at the point of attachment of the stabilizing fins 94 which are shown only in fragment.

Where the body shells are formed of a glass fiber filled resin, the mass of the target can be considerably reduced by forming the shells with extremely thin walls and internally reinforcing the thin walls of the body shells through the use of air under pressure introduced internally of the target by means of the air valve shown at 5. In this embodiment of the invention it is thus possible to form a target with walls of such a thickness that the target would, if not internally pressurized, collapse under the air loads imposed as the target is towed at high speed. Here the internal air pressure will, in eifect, reinforce the walls and rigidify them to the extent necessary to take the external loadings created by the movement of the target at high speeds.

In the form of the target shown in FIGURES 15 through 18 the body member 101, which is provided with a rotatable eye bolt 1'7, is formed of a plurality of identical body shells 102. The body shells in this form of the invention extend longitudinally of the completed body and are interconnected at longitudinally extending edges in the assembly of the target. The shells 1%2, here shown as four in number, are formed by a suitable molding process of preferably the same material used to form the body shells of the embodiment of the target shown in FIGURE 1. Each body shell 102, in the illustrated form of the presently described embodiment, thus forms a longitudinally arranged quarter of the target body.

In the now preferred practice of the present invention, each shell 1%2 is formed along the major extent of one edge thereof with an inset or joggle 103 which, in the assembly of the body member, receives the marginal portion 1% of the next adjacent shell 192. The contacting surfaces of the overlapping marginal portions of the shells are bonded together, as best shown in FIG- URE 17, to form a body member for the target of the desired configuration.

In this embodiment of the invention, the body shells 1112 are formed with integral formations which, when the shells are assembled, coact to form stabilizing fins 105 similar aerodynamicaliy to the fins of the previously described embodiments of the invention. To this end, the trailing portion of each body shell 1112 is formed with an integral extension 186 having a configuration somewhat V-shaped in cross section. As best illustrated in FIGURE 16 of the drawing, the integral extensions 1% of each body shell form contiguous faces of adjacent pairs of fins 1%.

The marginal edge portions of the extensions 1% are smoothly contoured as indicated at 167 and the abutting edge faces are bonded together with a suitable cement. A strip 1% of fabric or like material overlies the jointure and the strip in turn is bonded to the engaged surfaces of the extensions.

To internally reinforce the fins 135, a spider element 169 including a body member 111 and a plurality of leg members 112 may be used. The body member 111 is circular in form and of a diameter such that the peripheral edge thereof snugly engages the internal surface of the wall of the body member 101 at a preselected station thereon. The engaged edges are bonded to the body member and the member 111 thus forms a reinforcing bulkhead. The leg members 112, equal in number to the fins 10S, extend into the latter and are interlockingly engaged with a plurality of spaced shear webs 113, each having the marginal edge portion bonded to the interior surface of the extensions 106 forming a fin 105.

To permit the leg members 112 to be interlocked with the shear webs, it is now preferred to form the legs with spaced apart slots opening inwardly from the one edge thereof, the shear webs also being slotted whereby the leg and shear webs of each fin may be interfitted through engagement of the defining edges of the respective slots. The jointures thus formed may be reinforced and rigidified through a suitable bonding agent.

A tubular element 114, preferably of paper, is mounted transversely of each pair of diametrically opposed fins, the innermost shear web 113 of such pair of fins being apertured to pass the tubular element 114. The opposite end portions of the element 114 are each bonded to the inner faces of the outermost webs as best seen in FIGURE 15 of the drawing. These tubular elements reinforce the shear webs 113 and the latter, in turn, carry shear forces into the bulkhead formed by the body member 111, which as above explained is bonded to the walls of the body member 111. Thus, forces genl l erated in the fins are carried by the interlocking structural arrangement just described into the walls of the body member 101 of the target.

Here again, the fins formed when the body shells 102 are assembled produce rotation of the target about its longitudinal axis. As in the previously described embodiments of the target, this is brought about by so forming the integral formations 1% of each body shell so that they form, when the shells are assembled, the cambered fin formation necessary.

As in the earlier described form of the target, a reflector unit is used for reflecting exteriorly propagated or transmitted waves. The reflector unit of this embodiment of this invention is substantially similar to the reflector unit 21 and differs only in that support member 115 is formed with a plurality of circumferentially spaced grooves 116 for receiving the joggle N3 of the body shells 1%. It will also be seen that here again the support member 115 of the reflector is used to internally reinforce the body shells and augments the jointure between adjacent body shells in the assembled body member. This is accomplished here, as in the earlier described embodiments of the invention, by bonding the internal wall surfaces of the body shells 102 to the cylindrical surface defined by the support member 115 of the reflector unit.

Where found desirable and particularly in targets having a relatively long body length, the shells 102 may be formed of a plurality of sections longitudinally interconnected to form each of the body shells illustrated in FIGURE 15. Where the shells 102 are formed of multiple sections, these sections would be interconnected by joining the leading and trailing portions of longitudinally arranged sections by way of inset formations to form a jointure on the order of the joint illustrated in FIGURE 3 of the drawing.

It should now be seen that all embodiments of the present invention provide a target comprising a hollow body member of relatively thin walls and having a streamlined, elongate, aerodynamic configuration. The body member of the target, as it is formed of non-metallic frangible material, has a low volume-mass ratio for low inertia resistance to aircraft making inadvertent impact therewith, to avoid damage to the aircraft. The term mass as herein used is taken in the physic sense, i.e. as the measure or expression of quantity of matter in a body as indicated by the amount of force necessary to produce a given amount of motion in the body in a given time. The target of the present invention thus is one which can be used in fire control training programs with- .out fear that a collision between a target and the aircraft engaged in the program will result in destruction of the aircraft and death of the pilot. Although the target of the present invention will disintegrate if a collision does occur, yet the target carries a reflector unit which maintains a high reflectivity for exteriorly propagated waves such as used in radar systems without the necessity of employing any metallic structural parts. Although the reflector units used do include metallic foil, neither the foil nor the support member of the reflector unit present a hazard to an aircraft even if a collision should occur between the aircraft and the target.

All embodiments of the target herein shown can be produced through mass production methods at a cost considerably less than the cost of a target embodying structure of my previously filed application hereinbefore identified. This is particularly important as targets of the type herein disclosed are necessarily expendable in fire control training programs and are being used in ever increasing numbers.

A further feature of all embodiments shown arises through the use of non-metallic material for the body member. This permits the reflector unit to be carried internally of the body member so that the aerodynamic characteristics of the target may be maintained at the desired high level. It also should be appreciated that the type and arrangement of the reflector units can be varied without any change in the aerodynamic configuration of the target.

Although the now preferred embodiment of the present invention has been shown and described herein, it is to be understood that the invention is not to be limited thereto, for it is susceptible to changes in form and detail within the scope of the appended claims.

I claim:

1. An aerial tow target of the type described, comprising: a plurality of concavo-convex longitudinally extending body sections formed of a low density, low weight non-metallic material permeable by radar signals; means holding said sections assembled to form a hollow streamlined elongate body member having a low-drag aerodynamic stable configuration, said holding means being permeable by radar signals and including internal wall means for mounting and supporting a plurality of sheets of metallic foil, said wall means supporting said foil sheets to provide at least three normally intersecting reflecting surfaces for reflecting exteriorly propagated radar signals; said body sections including integral extensions forming, when said sections are assembled, stabilizing fins so contoured as to rotate said body member about its longitudinal axis in towed flight; and swivel means carried by said body member for attaching the latter to a tow line for tow by a towing aircraft.

2. An aerial tow target, comprising: a hollow, streamlined, elongate body member of an aerodynamically stable configuration, said body member being formed of at least two open ended body shells of light weight, low strength non-metallic material, each presenting at the open end thereof an internal cylindrical surface of like diameter; a plurality of sheets of metallic foil; means formed of a low density, non-metallic material having a relatively high volume, low weight ratio for mounting and supporting the plurality of said sheets in at least three normally intersecting planes, said mounting and supporting means providing an external cylindrical surface having a diameter substantially equal to the diameter of said internal cylindrical surfaces and telescopically fitted into the open ends of said body shells with the internal wall surfaces thereof bonded to the cylindrical surface of said mounting and supporting means thereby to longitudinally interconnect said shells to form said body member; and means carried by one of said body shells for attaching the said body member to a tow line for tow by a towing aircraft.

3. An aerial tow target, comprising: a hollow, streamlined, elongate body member having a low-drag aerodynamic configuration, said body member being formed of a plurality of interconnected, longitudinally arranged body shells formed of a light weight, non-metallic material permeable by radar waves; a reflector unit for reflecting exteriorly propagated radar waves; means formed of a low density non-metallic material having a relatively high volume low weight ratio for mounting and supporting said reflector unit, said support means carried internally of said body member and presenting a surface complementary to and engaged with the internal wall surface of said body member; means bonding said engaged surfaces to each other whereby said support means internally reinforces said body member and coacts with said body shell to augment the interconnection therebetween to hold said shells assembled; and means integral with said body shells forming a plurality of cambered fins spacedly carried by the trailing portion of said body member for aerodynamically rotating said body member about its longitudinal axis as it is towed in flight.

4. An aerial tow target of the type described, comprising: a hollow, thin-walled, streamlined, elongate body member having a low-drag aerodynamic configuration, the walls of said body member being formed of a non-metallic material impervious to air and having a low resistance to penetration by heavy objects making impact therewith, said body member having a low volume mass ratio for 13 low inertia resistance to avoid damage to aircraft making inadvertent impact therewith; easily fracturable low strength means defining a plurality of normally intersecting planes interiorly of said body and having surfaces for reflecting exteriorly propagated radar signals; means carried by said body member for attaching the latter to a tow line for tow by a towing aircraft; and means carried by said body member for introducing, interiorly of said body member, fluid under pressure whereby said body member may be pressurized, the internal fluid pressure reinforcing the walls of said body member without increasing the resistance of the material thereof to penetration by objects making impact therewith.

5. An aerial tow target of the type described, comprising: a hollow, thin-walled, streamlined, elongate body member of an aerodynamically stable configuration, the walls of said body member being formed of a nonmetallic material impervious to air and having a low resistance to penetration by heavy objects making impact therewith, said body member having a low volume mass ratio for low inertia resistance to avoid damage to aircraft making inadvertent impact therewith; fracturable means defining a plurality of normally intersecting planes interiorly of said body and having surfaces for reflecting exteriorly propagated radar signals; means carried by said body member for attaching the latter to a tow line for tow by a towing aircraft; means carried by said body member for introducing, interiorly of said body member, fluid under pressure whereby said body member may be pressurized, the internal pressure reinforcing the walls of said body member without increasing the resistance of the material thereof to penetration by objects making impact therewith; a plurality of cambered fins spacedly carried by said body member at the trailing end thereof; and means having a low impact resistance filling the trailing end portion of said body member and reinforcing the Walls thereof against forces induced thereinto by said fins in the towed flight of said target.

6. In a non-collision-hazardous tow target of streamlined configuration, the combination of: a body member comprising a thin walled shell of readily penetrable, nonmetallic material permeable by radar Waves including a tapered nose portion and a tapered tail portion, said shell comprising a plurality of sections bonded together; a radar wave reflector mounted within said shell; internal transverse reinforcement members spanning said shell and fixed to the walls thereof; fins mounted on said tapered tail portion, said fins being made of readily penetrable material and having a low mass-volume ratio; a relatively rigid transverse plate positioned in said nose portion; means connected to said plate for connection to a tow cable; and a mass of easily penetrable material confined in the forward end of said nose portion by said plate to transmit tow cable stresses from the plate into the walls of said shell.

7. A tow target comprising: a light weight, hollow, thin-Walled, streamlined structure having a tapered nose and having an aerodynamically stable configuration; transverse reinforcement means inside said structure at a location spaced rearwardly from said nose, said reinforcement means spanning the interior of the structure and fixed to the walls thereof to transmit stresses to said walls of the structure; an axial tension member extending rearward from said nose and attached to said transverse reinforcement means to transmit towing stresses thereto; and means rotatably connected to said tension member for connecting a tow line thereto with freedom for the structure to rotate relative to the tow line; and a plurality of fin elements carried by the trailing portion of structure so aerodynamically formed as to apply rotational forces to said structure as the target is towed.

8. An aerial tow target of the type described, comprising: a thin-walled, streamlined, elongate body member having low-drag aerodynamic characteristics and formed of a non-metallic material permeable by radar waves,

said body member having an extremely high volumeweight ratio to afford a relatively large target profile for a given weight and to minimize the force of impact in the event of a collision with an aircraft; reflector means carried internally of said body member presenting to externally propagated radar waves a predetermined radar reflectivity; said reflector means comprising low weight, low strength elements to avoid damage to aircraft inadvertently colliding with said tow target; swivel means carried by the leading portion of said body member for attaching the latter to a tow cable for tow by towing aircraft; and fin elements carried by the trailing portion of said body member for stabilizing said tow target in towed flight, said fin elements being so aerodynamically formed as to rotate said target relative to said tow cable in a towed flight of the target.

9. An aerial tow target as set forth in claim 8 in which said body member is formed of a molded paper pulp material impregnated with a water proofing compound.

10. An aerial tow target as set forth in claim 8 in which each of said fin elements is formed of a foamed plastic material having the root portion thereof secured to the trailing portion of said body member.

11. An aerial tow target, comprising: a plurality of non-metallic body shells having thin walls of an easily rupturable material permeable by radar waves; means for interconnecting said shells to form a hollow, elongate rigid body member of low-drag aerodynamic characteristics, at least one of said interconnecting means including means for mounting 10w strength reflector elements defining a plurality of normally intersecting planes interiorly of said interconnecting means and having metallic surfaces for reflecting exteriorly propagated radar waves, said interconnecting means being formed of an easily rupturable, non-metallic material so as to disintegrate if said target is struck by an aircraft in flight; swivel means carried by the leading portion of said body member for connection to the free end of a tow cable attached to an aircraft; and a plurality of fin elements carried by the trailing portion of said body member, said fins being so aerodynamically formed as to rotate said body member relative to said cable as said target is towed.

12. An aerial tow target of the type described, comprising: a plurality of concave-convex body sections formed of a low density, low-weight non-metallic material; means holding said sections assembled to form a hollow, streamlined, elongate body member having a low-drag aerodynamic configuration, said holding means including means permeable by radar waves presenting internal wall means for mounting and supporting a plurality of sheets of metallic foil, said wall means supporting said plurality of sheets of metallic foil to provide at least three normally intersecting reflecting surfaces for reflecting exteriorly propagated radar waves; stabilizing fins of a low density material carried by the aft portion of said body member, said fins being so aerodynamically formed as to rotate said body member about its longitudinal axis in towed flight; and swivel means carried by said body member for attaching the latter to a tow line for tow by a towing aircraft.

13. An aerial tow target, comprising: a plurality of thin-walled body shells of non-metallic material permeable by radar waves; means of a radar wave-passing material for interconnecting said shells to form a hollow, elongate, rigid body member having a low-drag aerodynamic configuration, said interconnecting means including wall means defining a plurality of normally intersecting recesses interiorly of said interconnecting means; a plurality of sheets of metallic foil mounted within said recesses and supported by the wall means defining the same, said sheets providing surfaces for reflecting exteriorly propagated radar waves, said interconnecting means being made of material permeable by radar waves and easily rupturable so as to disintegrate if said target is struck by an aircraft in flight; swivel means carried by the leading portion of said body member for connection to the free end of a tow cable attached to an aircraft; and a plurality of fin elements carried by the trailing portion of said body member, said fins being so aerodynamically formed as to rotate said body member as said target is towed.

14. An aerial tow target, camprising: a hollow, streamlined, elongate body member having a low-drag aerodynamical configuration, said body member being formed of a plurality of interconnected, longitudinally arranged, light weight, thin-walled body shells formed of a nonmetallic material; a reflector unit for reflecting exteriorly propagated radar waves; means formed of a low density, non-metallic material having a relatively high volume, low weight ratio for supporting said reflector unit, said support means carried internally of said body member and presenting a surface complementary to and engaged with the internal Wall surfaces of adjacent shells of said body member; means bonding said engaged surfaces to References Cited in the file of this patent UNITED STATES PATENTS 1,317,958 Clark Oct. 7, 1919 1,860,982 Binnie May 31, 1932 1,930,866 Warren Oct. 17, 1933 2,463,517 Chromak Mar. 8, 1949 2,525,332 Alger Oct. 10, 1950 2,591,016 Schoenherr Apr. 1, 1952 2,620,189 Livermon Dec. 2, 1952 

1. AN AERIAL TOW TARGET OF THE TYPE DESCRIBED, COMPRISING: A PLURALITY OF CONCAVO-CONVEX LONGITUDINALLY EXTENDING BODY SECTIONS FORMED OF A LOW DENSITY, LOW WEIGHT NON-METALLIC MATERIAL PERMEABLE BY RADAR SIGNALS; MEANS HOLDING SAID SECTIONS ASSEMBLED TO FORM A HOLLOW STREAMLINED ELONGATE BODY MEMBER HAVING A LOW-DRAG AERODYNAMIC STABLE CONFIGURATION, SAID HOLDING MEANS BEING PERMEABLE BY RADAR SIGNALS AND INCLUDING INTERNAL WALL MEANS FOR MOUNTING AND SUPPORTING A PLURALITY OF SHEETS OF METALLIC FOIL, SAID WALL MEANS SUPPORTING SAID FOIL SHEETS TO PROVIDE AT LEAST THREE NORMALLY INTERSECTING REFLECTING SURFACES FOR REFLECTING EXTERIORLY PROPAGATED RADAR SIGNALS; SAID BODY SECTIONS INCLUDING INTEGRAL EXTENSIONS FORMING, WHEN SAID SECTIONS ARE ASSEMBLED, STABILIZING FINS SO CONTOURED AS TO ROTATE SAID BODY MEMBER ABOUT ITS LONGITUDINAL AXIS IN TOWED FLIGHT; AND SWIVEL MEANS CARRIED BY SAID BODY MEMBER FOR ATTACHING THE LATTER TO A TOW LINE FOR TOW BY A TOWING AIRCRAFT. 